In my current job, I've participated in several search committees. After we review the resumes and decide who we want to interview, we determine the days and times when all of us are available. The head of the search committee will then email the candidates to offer them the various time slots. So to me, I've always assumed that's the “normal” way of doing it. But now that I've been job hunting myself (after being at my current place for several years), I see that everyone does it differently.
Sometimes the employer will email me and say, “We have these time slots, so please let us know if any of these work for you.” But sometimes they will only give me one day and time, which really irks me.
For example, I just got an email from a potential employer saying “We'd like to interview you on Thursday the 26th at 11am. Please confirm that you can make it.” It wasn't even phrased as a question – just a statement that this is when the interview is, take it or leave it. (Well, they didn't say that last part, but I feel like that was the implication.)
Luckily, my current employer knows that I am job hunting and they are really good about letting me take time off on short notice. But what if someone doesn't have that luxury? Obviously the employer is the one in the position of power here, so I have to play the game their way.